CN111832185B - Accurate assembly simulation method and system based on skin model - Google Patents
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Abstract
The present disclosure provides a method and a system for accurate assembly simulation based on a skin model, which are used for generating a skin model of a part according to shape, position and direction tolerances and identifying a matching surface and load boundary conditions of the skin model of the part in order to combine geometric tolerances of a workpiece in assembly simulation; modeling the SMS-based multi-body assembly in terms of geometric tolerances using a quadratic optimization method and determining the relative position of the mating surfaces, the contact points being subjected to additional load and further deformed, and subsequently the relative positioning of the parts being moved further due to the contact deformation; if a new contact point is generated, another iteration of the second optimization will begin using the deformed SMS and reduced load; after balancing all loads, iteration is stopped, all parts are assembled, and accurate assembly simulation of a plurality of parts is realized; meanwhile, by repeating the assembly simulation for a plurality of times, effective tolerance analysis can be performed according to the obtained assembly deviation.
Description
Technical Field
The disclosure belongs to the technical field of assembly simulation, and particularly relates to a skin model-based accurate assembly simulation method and a skin model-based accurate assembly simulation system.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
Geometric tolerances on each manufactured workpiece are unavoidable with respect to manufacturing errors and measurement uncertainties. In order to ensure that on these basis there is still part interchangeability in large-scale assembly, the concept of geometric tolerances is defined, the limits of geometric tolerances are specified from the assembly point of view, furthermore, the functional requirements of the artefact depend on the influence of tolerance stack-up; thus, establishing reasonably accurate tolerances is a critical task that can ensure the function and quality of the manufacturing process while optimizing production costs and respecting manufacturing tools; the geometry and tolerance (GD & T) scheme should be implemented in an early design process, the purpose of which is to ensure adequate product quality in terms of manufacturing and inspection costs associated with tolerances by defining limitations of geometric defects of manufacture.
The inventors have found that in most commercial Computer Aided Tolerance (CAT) systems, the geometric tolerance is created by converting an ideal curved surface, which lacks an understanding of the mechanism and form of the geometric tolerance and is therefore inconsistent with international tolerance standards (i.e., GD & T and ISO Geometric Product Specification (GPS) standards); in addition, this approximation does not meet the need for precise prediction of assembly tolerances, particularly for high precision assembly; and is insufficient to cover geometric tolerances throughout the product life cycle; assembly simulation is one of the most important problems in the product design process, and is the basis of tolerance analysis; these tolerances caused by shape defects can be classified into shape tolerances, orientation tolerances and position tolerances during the design process; in order to improve the accuracy of tolerance analysis and integration, the factors must be considered and integrated into the assembly simulation modeling; the inventor finds that the prior assembly simulation method ignores the comprehensive influence of geometric tolerance and contact deformation, and the geometric tolerance can be generated in the manufacturing process, and the contact deformation can be generated in the assembling process, so that the assembly quality can be influenced by the geometric tolerance and the contact deformation; during assembly, the two interact and affect the final assembly quality.
Disclosure of Invention
In order to solve the problems, the present disclosure provides a precise assembly simulation method and system based on a skin model, which effectively improves the accuracy of assembly simulation by considering the influence of contact deformation and geometric tolerance on workpiece assembly, and meanwhile, performs tolerance analysis according to the assembly simulation result to obtain reasonable geometric tolerance, provides guidance for geometric tolerance of workpiece production, effectively avoids contact deformation generated in the workpiece assembly process, and improves assembly quality.
According to a first aspect of the embodiments of the present disclosure, there is provided a skin model-based accurate assembly simulation method, including:
collecting structural parameters of a workpiece to be assembled;
generating a skin model of the workpiece to be assembled based on structural parameters and geometric tolerances of the workpiece to be assembled;
defining the matching surface and load boundary conditions of a skin model of a workpiece to be assembled;
equivalent assembly of a skin model of a workpiece to be assembled to calculation of displacement and reaction force of the matching surfaces, and definition of a distance objective function between the matching surfaces and constraint conditions of the distance objective function;
and carrying out iterative computation on the objective function to minimize the distance between the matching surfaces and obtain an assembly simulation result.
According to a second aspect of embodiments of the present disclosure, there is provided a skin model-based precision assembly simulation system, comprising:
the model construction module is used for collecting structural parameters of the workpiece to be assembled; generating a skin model of the workpiece to be assembled based on structural parameters and geometric tolerances of the workpiece to be assembled; defining the matching surface and load boundary conditions of a skin model of a workpiece to be assembled;
the objective function construction module is used for equivalent assembly of the skin model of the workpiece to be assembled to calculation of the displacement and the reaction force of the matching surfaces, and defining a distance objective function between the matching surfaces and constraint conditions of the distance objective function;
and the assembly simulation module is used for carrying out iterative computation on the objective function so as to minimize the distance between the matching surfaces and obtain an assembly simulation result.
Compared with the prior art, the beneficial effects of the present disclosure are:
(1) According to the scheme, the real part with the shape defect is simulated by means of the skin model, geometric tolerance and local contact deformation are considered in the assembly simulation process, the fact that equivalent ideal surfaces are used for replacing matched non-ideal surfaces is avoided, the accuracy of assembly simulation can be affected by the equivalent surfaces, and the application in shaft hole assembly is prevented; the scheme disclosed by the disclosure can consider that the contact of the matching surfaces is frictional, which is consistent with the actual situation, and meanwhile, the simulation problem of multi-part assembly is solved; reasonable geometric tolerance is obtained through assembly simulation, guidance is provided for the geometric tolerance of workpiece production of manufacturers, contact deformation generated in the workpiece assembly process is effectively avoided, and assembly quality is improved.
(2) The scheme of the present disclosure requires more computational efficiency than existing finite element methods; currently, the finite element method is reliable for simulating localized contact deformations in an assembly; however, for Monte Carlo simulations, pre-processing the randomly generated skin model in finite element analysis is ineffective.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate and explain the exemplary embodiments of the disclosure and together with the description serve to explain the disclosure, and do not constitute an undue limitation on the disclosure.
FIG. 1 is a flow chart of a method for simulating accurate assembly based on the shape of a skin model according to a first embodiment of the present disclosure;
FIG. 2 (a) is a schematic diagram of an initial model of a workpiece according to a first embodiment of the disclosure;
FIG. 2 (b) is a schematic diagram of a segmented workpiece model according to one embodiment of the disclosure;
FIG. 2 (c) is a schematic diagram of a workpiece model after geometric tolerance addition treatment according to the first embodiment of the disclosure;
FIG. 2 (d) is a diagram illustrating the results of the skin model after reorganization according to the first embodiment of the present disclosure;
FIG. 3 (a) is a schematic diagram illustrating the relative positional relationship of two mating surfaces according to the first embodiment of the disclosure;
fig. 3 (b) shows a view of a line along the normal direction (n j+1,i ) Projection to S j+1 Schematic of the upper closest projection;
FIG. 4 (a) is a schematic diagram showing interaction mechanism of contact force and deformation after an external load is applied according to the first embodiment of the present disclosure;
FIG. 4 (b) is a schematic diagram showing the interaction mechanism of the contact force and deformation after the application of an external load to create a new contact point according to the first embodiment of the present disclosure;
FIG. 4 (c) is a schematic diagram illustrating the interaction mechanism of the contact force and deformation after another external load is applied according to the first embodiment of the present disclosure;
FIG. 4 (d) is a schematic diagram illustrating the interaction mechanism of the contact force and deformation after applying another external load to create a new contact point according to the first embodiment of the present disclosure;
FIG. 5 is a flowchart of an iterative algorithm for contact deformation according to one embodiment of the present disclosure;
FIG. 6 is a schematic diagram of a simulation example of a specific apparatus according to a second embodiment of the disclosure;
fig. 7 is a schematic diagram of whether the influence of contact deformation on the X distribution is considered.
Detailed Description
The disclosure is further described below with reference to the drawings and examples.
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments in accordance with the present disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Embodiment one:
the embodiment aims to provide an accurate assembly simulation method based on a skin model.
A skin model-based accurate assembly simulation method comprises the following steps:
collecting structural parameters of a workpiece to be assembled;
generating a skin model of the workpiece to be assembled based on structural parameters and geometric tolerances of the workpiece to be assembled;
defining the matching surface and load boundary conditions of a skin model of a workpiece to be assembled;
equivalent assembly of a skin model of a workpiece to be assembled to calculation of displacement and reaction force of the matching surfaces, and definition of a distance objective function between the matching surfaces and constraint conditions of the distance objective function;
and carrying out iterative computation on the objective function to minimize the distance between the matching surfaces and obtain an assembly simulation result.
Further, the structural parameters comprise conventional parameters such as workpiece size, curve parameters and lines;
a flowchart illustrating a skin model shape-based accurate assembly simulation method according to the present disclosure is shown in fig. 1, in order to incorporate geometric tolerances of a workpiece in an assembly simulation, the geometric tolerances are specified according to product design requirements; generating a skin model SMS (skin model shapes) of the part based on shape, position and orientation tolerances; identifying mating surfaces of SMS and load boundary conditions including points of application, magnitude and direction of applied force and torque, location and direction of constraints using GeoSpelling, a formal language for expressing canonical semantics; modeling the SMS-based multi-body assembly with a quadratic optimization method in terms of geometric tolerances and determining the relative position of the mating surfaces, as explained by the Hertz theory, the contact points are subjected to additional load and are further deformed, and then the relative positioning of the parts will be moved further due to the contact deformation; if a new contact point is generated, another iteration of the second optimization will begin using the deformed SMS and reduced load; after all loads are balanced, iteration is stopped, all parts are assembled, and accurate assembly simulation of a plurality of parts is realized.
It should be clear to those skilled in the art that geometric tolerances are a combination of systematic and random deviations, the characteristics of which are deterministic, predictable and reproducible; in contrast, unpredictable fluctuations in the manufacturing process can produce random deviations; the tolerance of the design, which is specified by the designer according to the product design requirements, may limit the geometric tolerance. To control the quality and function of the assembly; thus, the present disclosure generates SMS using geometric tolerances of the workpieces to be assembled, the geometric tolerances specified by the designer according to the product design requirements; a representative workpiece surface profile is generated based on SMS of the geometric tolerance to approximate the actual surface.
Specifically, the skin model generation process specifically includes the following steps:
SMS for geometric tolerance modeling can be created by mathematical methods (e.g., second order shape and random field methods) or by results of manufacturing process simulations or part prototype measurements; in the embodiment, the part prototype measurement result is adopted to create the skin model, and the equivalent skin model surface needs to be ensured to be consistent with a specified tolerance, wherein the specified tolerance is specified by a designer according to the design requirement of a product; the generation of the skin model requires firstly dividing the workpiece structure to independently process each surface; each surface is accompanied by geometric tolerances that are based on design tolerances; different tolerances may limit different kinds of geometric features, e.g. shape tolerances may limit inherent features, while orientation and position tolerances may limit situation features; in skin model construction, geometric tolerances are added to the original nominal model in a merged manner when they are simulated; the components of the skin model go through three steps: segmentation, geometric tolerance addition and reorganization; as shown in fig. 2 (a), a skin model with specified tolerances will be generated; the non-flatness of the SMS described in fig. 2 (b) -2 (d) has been scaled to ease the viewing of geometric tolerances, and other modeling issues-non-connection, face connection, definition of obtuse and acute dihedral angles, and definition of grid dimensions and bias sizes are well known to those skilled in the art and will not be described in detail herein.
Furthermore, the fitting simulation method equates the fitting of SMS to the calculation of the displacement and the reaction force of the mating surfaces, and defines an objective function of the distance between the mating surfaces and the constraint condition thereof, and specifically comprises the following steps:
on the mating surface, the contact deformation and the relative position are mutually dependent, and the contact point is determined by the relative position of the mating surface; however, the relative position of the mating surfaces varies with contact deformation, in order to accelerate the solving speed of the relative position, assuming that SMS is rigid, small displacement torsion theory (SDT) is used for rigid body displacement theory for calculating the initial contact point between the two skin surfaces; in SDT theory, the surface displacement in terms of center point is as follows:
SDT＝[r t] T ＝[α β γ u v w] T
(1)
wherein r and t are rotation and translation of the rigid body, respectively, r comprises three rotation angles α, β and γ around the x, y and z directions, respectively; u, v and w are translations in x, y and z directions, respectively;
in the field of tolerance design, the displacement is usually small and is usually linear, for discrete surfaces S j Any normal of (2)Vector n j,i After a rigid body displacement, its direction will change as follows:
n' j，i ＝n j，i -n j，i ×r j (2)
the distance between the mating surfaces is a basic constraint that addresses the initial contact point; for the surface S j Vertex A of the upper part j,i It is along the normal direction (n j+1,i ) Projection to S j+1 Upper closest projection a j+1,i As shown in FIG. 3 (a), S j,i And A j+1,i Distance d between j,i Can be expressed as:
distance d 'after displacement' j,i The method comprises the following steps:
ignoring the second order term, the distance d 'of the displacement is calculated' j,i Linearization was performed and the results of linearization are shown below:
wherein C is j And C j+1 Respectively S j And S is j+1 Is defined by a center point of (2);
thus, for the entire workpiece, the distance constraints may be reorganized in a matrix as follows: d' =a·sdts+d
(6)
Because rigid body displacement theory is adopted, the interpenetration between the matching surfaces is not ensured, thus d' j,i Should be greater than or equal to zero.
Further, the determining of the balance constraint specifically includes:
for each SMS, the contact points are responsible for carrying internal and external loads; during assembly, the external force F, the external torque T and the internal or support reaction force R should be balanced, and the balancing constraint can be expressed as:
wherein j represents different surfaces to be assembled, i is different discrete points on the surface j, k is the sequence number of the force applied by the surface j, q is the sequence number of the torque applied by the surface j, L j,i Is the distance between the force point and the center of the object, most previous studies were based on the assumption of friction-free, non-adhesive contact; however, friction greatly affects the accuracy of the assembly simulation, and can also be controlled by selecting less than μR j,i (μ is a friction coefficient) and a value in a tangential direction of a contact point, which is modeled using equation (7); as another constraint, d' j,i The value of (2) should be greater than or equal to zero, in addition, if the distance d' j,i Greater than zero, the reaction force R j,i The value of (2) is accordingly zero; if R is j,i Greater than zero, d' j,i =0; thus, the combined constraint of the distance constraint and the balance constraint can be expressed as:
R T d'＝0
(8)
hereafter, the assembly simulation of SMS is equivalent to finding the displacement SDT and the reaction force R that minimize the distance between the mating surfaces and satisfy the above constraints, as follows:
in addition, the problem is reorganized in a matrix form of secondary targets and secondary constraints, i.e
The above problem can be solved by a quadratic optimization algorithm, and in order to increase the solving speed, the present embodiment adopts a Hessian function for calculating the quadratic objective lens to solve.
Further, since the influence of the local contact deformation on the stack-up deviation is not negligible with an increase in the assembly load, since the contact deformation caused by the external load on the mating surface shows a change in topology, it is important to determine the influence of the local contact deformation on the assembly deviation;
with an external load applied, as shown in FIG. 4 (a), a reaction force R between two contact points 1 j,i The resulting deformation delta 1 j,i And delta 1 j+1,i Another contact point may be generated as shown in fig. 4 (b). Only a much smaller delta is allowed since newly generated contact points are prevented 1 ' j,i Deviation. Delta then 1 ' j,i And delta 1 ' j+1,i The sum of the allowance of (d) 1 min ，d 1 min Also the minimum distance of the mating surfaces, except for zero distance at the contact points, i.e. when an external load is applied, as shown in fig. 4 (a), between the contact points by the reaction force R 1 j,i The resulting deformation delta 1 j,i And delta 1 j+1,i Other contact points may be generated as shown in fig. 4 (b). Only a much smaller delta is allowed due to the resistance from the newly created contact point 1 ' j,i And (5) deformation. Delta 1 ' j,i And delta 1 ' j+1,i The sum of the allowance of (d) 1 min ，d 1 min Also the minimum distance of the contact surface, the distance of the contact point is zero, i.e
The contact deformation depends on the reaction force. Accordingly, the reaction force R 1 j,i Reduced to R 1 ' j,i This does not meet the load boundary constraint; the next round of interaction between the reaction force and the contact deformation is an unbalanced external force R 2 j,i Initially, as shown in fig. 4 (c). The newly found contact point will deform fig. 4 (d) in the second iteration.
On the basis of studying the correlation between reaction force and contact deformation, we propose an iterative method to evaluate the relative position of assembled SMS with contact deformation, as shown in fig. 5. It can be used to determine the local surface deformation caused by the displacement of each point on the non-ideal surface. In general, the basic theory for assessing elastic contact problems is hertz theory. Based on Hertz theory, elastic deformation delta of single contact point in the r-th iteration r j,i The following can be calculated:
wherein R is r j,i And ρ r j,i The reaction force and the average curvature at the contact point of the surface, E j Is S j Elastic modulus of (a). Due to R r j+1,i Equal to R r j,i Thus, delta can be determined using equation (12) r ' j+1,i Replaced by delta r ' j,i Then
If the mating surfaces have the same material properties, equation (13) can be simplified as follows:
wherein delta is r ' j,i Is the temporary displacement of the contact point in the r-th iteration. After one iteration, the SMS is deformed accordingly. In this case, only the external force F r j,k A part of the reaction force R 'which is reduced' j,i Balance. For deformed SMS, unbalanced forces and torques are imported into the next iteration as load boundary constraints. The graph of this step is highlighted in gray in fig. 5, and then the next round of secondary optimization is started, and the iterative process will continue until all external forces and torque are balanced.
Embodiment two:
it is an object of the present embodiment to provide a skin model based accurate assembly simulation system.
A skin model-based precision assembly simulation system, comprising:
the model construction module is used for collecting structural parameters of the workpiece to be assembled; generating a skin model of the workpiece to be assembled based on structural parameters and geometric tolerances of the workpiece to be assembled; defining the matching surface and load boundary conditions of a skin model of a workpiece to be assembled;
the objective function construction module is used for equivalent assembly of the skin model of the workpiece to be assembled to calculation of the displacement and the reaction force of the matching surfaces, and defining a distance objective function between the matching surfaces and constraint conditions of the distance objective function;
and the assembly simulation module is used for carrying out iterative computation on the objective function so as to minimize the distance between the matching surfaces and obtain an assembly simulation result.
Embodiment III:
an object of the present embodiment is to provide a tolerance analysis method based on a skin model.
The tolerance analysis method based on the skin model adopts the accurate assembly simulation method based on the skin model, carries out tolerance analysis according to assembly deviation distribution conditions by repeating the accurate assembly simulation method for a plurality of times, carries out tolerance analysis on a workpiece by utilizing the assembly deviation distribution conditions, further provides accurate geometric tolerance guidance for the workpiece production process, and improves the workpiece assembly quality.
In particular, in this embodiment, monte carlo simulations are used to show how geometric tolerances and local contact deformations affect the values of functional requirement X, the final objective being to compare the cumulative assembly deviations of the deformed mating surfaces and the undeformed surfaces; by performing a tolerance analysis based on Monte Carlo simulation to show the effect of geometric tolerances and local contact deformation on assembly deviations; one simulation considers only the effects of geometric tolerances, the other considers the effects of both deviations; FIG. 6 shows an example of an assembly simulation of an assembly named RGB assembly consisting of three planar sections with a mating face tolerance of 0.3 mm; functional requirements (x=100±1.50 mm) were defined between faces Gr and B8, and 1000 simulations were performed; wherein the functional requirement is assembly deviation.
As depicted in fig. 7, a distribution of X from 1000 simulations is shown, using an initial tolerance value (tp=0.3 mm and tf=0.3 mm) and taking into account tolerance analysis of part deformation, indicating that X meets the functional requirement; to show the effect of contact deformation, the distribution of X was calculated in the same 1000 simulated runs without contact deformation, as shown in fig. 7, the contact deformation exhibited a considerable effect on X, indicating that the effect of contact deformation is not negligible in this example; however, the mating surfaces flatten out due to the assembly forces, so that tolerance values can be defined to a greater extent than conventionally defined, which also ensures that X meets the functional requirements; moreover, larger tolerances can greatly reduce manufacturing costs; in particular, for an assembled body composed of a large number of parts, the assembly deviation analysis based on assembly simulation will certainly be more important. In addition, in 1000 monte carlo simulations, the average time consumption per run considering the contact deformation is 90s, and the scheme of the present disclosure has higher execution efficiency compared to FEM.
The accurate assembly simulation method and the accurate assembly simulation system based on the skin model, which are provided by the embodiment, can be completely realized, and have wide application prospects.
The foregoing description of the preferred embodiments of the present disclosure is provided only and not intended to limit the disclosure so that various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
While the specific embodiments of the present disclosure have been described above with reference to the drawings, it should be understood that the present disclosure is not limited to the embodiments, and that various modifications and changes can be made by one skilled in the art without inventive effort on the basis of the technical solutions of the present disclosure while remaining within the scope of the present disclosure.
Claims (10)
1. The accurate assembly simulation method based on the skin model is characterized by comprising the following steps of:
collecting structural parameters of a workpiece to be assembled;
generating a skin model of the workpiece to be assembled based on structural parameters and geometric tolerances of the workpiece to be assembled;
defining the matching surface and load boundary conditions of a skin model of a workpiece to be assembled;
equivalent assembly of a skin model of a workpiece to be assembled to calculation of displacement and reaction force of the matching surfaces, and definition of a distance objective function between the matching surfaces and constraint conditions of the distance objective function;
performing iterative computation on the objective function to minimize the distance between the matching surfaces and obtain an assembly simulation result;
wherein, when an external load is applied, a reaction force R between the two contact points 1 j,i The resulting deformation delta 1 j,i And delta 1 j+1,i Between contact points by reaction force R 1 j,i The resulting deformation delta 1 j,i And delta 1 j+1,i Other contact points are generated, only delta is allowed 1 ' j,i Deformation, delta 1 ' j,i And delta 1 ' j+1,i The sum of the allowance of (d) 1 min ，d 1 min Is also the minimum distance of the mating surfaces; when another external load is applied, only delta is allowed 1 ' j,i Deformation, delta 1 ' j,i And delta 1 ' j+1,i The sum of the allowance of (d) 1 min ，d 1 min Also the minimum distance of the contact surface, the distance of the contact point is zero, i.e
Elastic deformation delta of single contact point in the r-th iteration r j,i The following can be calculated:
wherein delta is r ' j,i Is the temporary displacement of the contact point in the r-th iteration ρ r j,i And ρ r j+1,i Representing the average curvature of the surface contact points, E j And E is j+1 The elastic modulus is shown.
2. The skin model-based accurate assembly simulation method according to claim 1, wherein the generation of the skin model is realized through segmentation, geometric tolerance addition and recombination.
3. A skin model based accurate assembly simulation method according to claim 2, wherein the segmentation is to divide the created workpiece model into independent surfaces for separate processing, the geometric tolerance attachment is to add a specified tolerance to each surface, and the recombination is to recombine the divided surfaces according to the positional relationship of the original model.
4. The skin model-based accurate assembly simulation method according to claim 1, wherein the constraint conditions comprise a distance constraint and a balance constraint.
5. The method of claim 4, wherein the distance constraint is applied to a contact point determined by the relative positions of mating surfaces of the skin model of the workpiece to be assembled, the contact point being a basic condition for solving the distance between the mating surfaces.
6. The method for simulating accurate assembly based on skin model according to claim 1, wherein the relative position of the mating surface changes with the contact deformation, and in order to increase the solving speed of the relative position, it is necessary to assume that the skin model is rigid deformation, and the contact point is calculated by small displacement torsion theory SDT.
7. A method of simulation of accurate assembly based on skin models according to claim 1, characterized in that for each part skin model to be assembled, the contact points are responsible for bearing internal and external loads, so that during assembly, external forces F, external torque T and supporting reaction forces R should be balanced, the balancing constraints being expressed as:
wherein j represents different surfaces to be assembled, i is different discrete points on the surface j, k is the sequence number of the force applied by the surface j, q is the sequence number of the torque applied by the surface j, L j,i Is the distance between the force point and the center of the object.
8. The skin model-based accurate assembly simulation method according to any one of claims 1 to 7, wherein the skin model-based accurate assembly simulation method is adopted to perform assembly simulation for a plurality of times to obtain assembly deviation distribution conditions, tolerance analysis is performed on a workpiece by using the assembly deviation distribution conditions, so that accurate geometric tolerance guidance is provided for a workpiece production process, and workpiece assembly quality is improved.
9. A skin model-based precision assembly simulation system, comprising:
the model construction module is used for collecting structural parameters of the workpiece to be assembled; generating a skin model of the workpiece to be assembled based on structural parameters and geometric tolerances of the workpiece to be assembled; defining the matching surface and load boundary conditions of a skin model of a workpiece to be assembled;
the objective function construction module is used for equivalent assembly of the skin model of the workpiece to be assembled to calculation of the displacement and the reaction force of the matching surfaces, and defining a distance objective function between the matching surfaces and constraint conditions of the distance objective function;
the assembly simulation module is used for carrying out iterative computation on the objective function so as to minimize the distance between the matching surfaces and obtain an assembly simulation result;
wherein, when an external load is applied, a reaction force R between the two contact points 1 j,i The resulting deformation delta 1 j,i And delta 1 j+1,i Between contact points by reaction force R 1 j,i The resulting deformation delta 1 j,i And delta 1 j+1,i Other contact points are generated, only delta is allowed 1 ' j,i Deformation, delta 1 ' j,i And delta 1 ' j+1,i The sum of the allowance of (d) 1 min ，d 1 min Is also the minimum distance of the mating surfaces; when another external load is applied, only delta is allowed 1 ' j,i Deformation, delta 1 ' j,i And delta 1 ' j+1,i The sum of the allowance of (d) 1 min ，d 1 min Also the minimum distance of the contact surface, the distance of the contact point is zero, i.e
Elastic deformation delta of single contact point in the r-th iteration r j,i The following can be calculated:
wherein delta is r ' j,i Is the temporary bit of the contact point in the r-th iterationShift ρ r j,i And ρ r j+1,i Representing the average curvature of the surface contact points, E j And E is j+1 The elastic modulus is shown.
10. The skin model based precision assembly simulation system of claim 9, wherein the generation of the skin model is accomplished through segmentation, geometric tolerance addition and reassembly.
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